This invention relates to a negative electrode for high-energy lithium-ion batteries, including an electrode composition, containing a lithium intercalation compound, a conductive agent and a polymer binder, on a metallic support substrate. The invention also relates to the production of such a negative electrode.
Such batteries typically contain lithium-containing metal oxides of metals Mn, Ni, Cr or Co or mixed oxides of these metals as the cathode material in a mixture with binders such as, e.g., fluoropolymers, preferably polytetrafluoroethylene (PTFE) or dispersions thereof and conductive agents (carbon blacks, graphites) (JP-A-236258/1988, U.S. Pat. No. 5,707,763), which are applied to metallic conductor materials. Various types of carbon are used as active anode materials. These are applied, as a mixture with binders and optionally with conductive materials, to a metallic support with the aid of a coating device (see EP 0 710 995 A2 or DE 196 33 463 A1). WO 97/32347 discloses fluoropolymers such as polyvinylidene difluoride (PVDF) or PVDF/acrylate graft polymers as binder for fixing the active materials to the metallic support material.
WO 97/15087 discloses a process for producing anodes for a high-energy battery, in which the carbon compositions are introduced into porous nickel support materials, preferably Ni foam. Such Ni foam substrates are obtained by first pre-nickeling polyurethane foams in an Ar plasma, then precipitating metallic nickel from a salt solution (sols) and, lastly, breaking down the polyurethane by exposure to high temperatures (about 800-1000xc2x0 C.).
Large high-energy cells with a prismatic structure or in the form of cylindrical cells with energy capacities of from 6 to 80 Ah, which contain lithium-containing Me oxides as cathode material and carbon as anode material (lithium-ion cells), are primarily intended to be used in satellites and batteries for electrical road vehicles. These battery types are distinguished by the fact that they contain a relatively low proportion of chemically inactive metallic conductor materials and, therefore, have a high battery energy density of 100-120 Wh/kg (power density 185 W/kg).
High-energy batteries generally contain pasted Ni-foam/carbon anodes, which generally have the active materials at a small distance from the metallic conductor. This characteristic is partly responsible for the fact that it is possible to discharge the electrodes, or the batteries made with them, with currents of from C/20 (forming current) to 5 C. In this case, 1 C denotes the current theoretically needed to discharge the maximum battery capacity fully within one hour.
Thus, an object of the invention is to provide negative electrodes for high-energy lithium-ion batteries, and a process for their production.
In one aspect the invention is a negative electrode for high-energy lithium-ion batteries including an electrode composition containing a lithium intercalation compound, a conductive agent, a latex additive based on an acrylic acid derivative copolymer and a polymer binder containing butadiene units, and a metallic support substrate.
In another aspect, the invention is a process for producing a negative electrode including mixing a conductive agent with an acrylic acid derivative copolymer latex additive to form a homogenized mixture, dispersing the homogenized mixture in a solvent, mixing the homogenized mixture and the solvent with a lithium intercalation compound to form a homogenous composition, mixing the homogenous composition with a polymer binder containing butadiene units to form an electrode composition, and applying the electrode composition to a metallic support substrate.